Local Sites

Distribution of landmasses of the Paleo-Earth

posted Jul 6, 2011, 8:35 AM by Abel Mendez

Our planet shows different features as it rotates along its axis, sometimes dominated by land and others by ocean. Land areas are distributed predominantly in the Northern Hemisphere (68%) relative to the Southern Hemisphere (32%) as divided by the equator. Coincidentally, the same can be say about the East-West distribution with most in the Eastern Hemisphere (68%) relative to the Western Hemisphere (32%). These hemispheres are divided by an imaginary circle crossing -20° longitude (20°W), which makes the Eastern Hemisphere center at 73° longitude (73°E). As Earth evolved through time these numbers changed dramatically.

If we focus on East-West areas, two distinctive interpretations can be defined: the side associated with more continental area, the Maximum Facing Area (MFA), and the side associated with more apparent (normal) area, the Maximum Normal Area (MNA). The MFA is sort of East-West hemisphere area division while the MNA is based on the apparent viewable area as a disk. In practice, the longitudinal location of the MFA and MNA are close, but not necessarily the same.

The MFA is normalized based of the total continental area available in the planet while the MNA is normalized to the total area of the disk (without prior knowledge of the global land area). For example, a MFA of 68% means that 68% of the land area is in one side of the planet, while a MNA of 42% means that up to 42% of the planet's disk area is covered by land at any moment. Therefore, the MNA is somewhat related to the maximum diurnal albedo of the planet as land areas are usually brighter than ocean areas, although clouds tent to minimize the effect.

Table 1 shows the North-South and East-West analysis of the land areas of Earth's past derived from our Visible Paleo-Earth project datasets. Figure 1 shows the hemisphere of Earth with more apparent area (MNA) in the last 750 million years (the actual longitude value of this side is show in the last column of Table 1). Figure 2 shows the full analysis for current Earth, other periods and further analysis of Table 1 results are available here (some of the previous values were slightly corrected in Table 1). We are using the curves of the Normal Area (i.e. Figure 1, c) to correlate Earth's albedo with land areas, a procedure that will be important to interpret future light curves from Earth-like exoplanets.

Table 1. Distribution of land areas of Earth in the last 750 million years. The global land coverage varied little within 10 to 30%, however, there where large transitions from South to North (Late Triassic, 220 Mya) and from East to West (Early Devonian, 400 Mya). Also, note the extreme clustering of over 95% of the land areas in one side of the planet (MFA) during Pangea (Middle Triassic, 240 Mya) and Rodinia (Precambrian, 750 Mya).

Age(Mya)

Age Name

Land

(%)

Ocean

(%)

Land N

(%)

Land S

(%)

MFA(%)

F-lon(°)

MNA(%)

N-lon(°)

000

Present

29

71

68

32

68

73

42

59

020

Early Miocene

30

70

68

32

68

70

44

59

035

Late Eocene

29

71

66

34

69

20

41

53

050

Early Eocene

28

72

64

36

72

29

39

50

065

Late Cretaceous (K-Pg)

26

74

61

39

77

28

39

10

090

Late Cretaceous

23

77

53

47

83

36

35

-5

105

Early Cretaceous

24

76

54

46

86

40

39

-4

120

Early Cretaceous

26

74

57

43

90

41

46

0

150

Late Jurassic

25

75

58

42

92

36

49

2

170

Middle Jurassic

26

74

57

43

94

35

52

5

200

Late Triassic

27

73

53

47

95

33

59

3

220

Late Triassic

28

72

52

48

96

37

62

5

240

Middle Triassic

27

73

42

58

98

41

58

8

260

Late Permian

26

74

39

61

94

41

59

10

280

Early Permian

25

75

39

61

93

30

57

9

300

Late Pennsylvanian

21

79

34

66

90

35

45

8

340

Middle Mississippian

20

80

25

75

86

48

40

4

370

Late Devonian

19

81

20

80

90

56

30

13

400

Early Devonian

21

79

13

87

69

74

31

-2

430

Middle Silurian

19

81

18

82

61

-162

27

160

440

Early Silurian

19

81

15

85

75

-176

32

170

450

Late Ordovician

19

81

15

85

71

-175

30

174

470

Middle Ordovician

19

81

17

83

74

-144

33

176

500

Late Cambrian

23

77

17

83

79

-139

42

179

540

Early Cambrian

27

73

20

80

80

-153

53

176

560

Late Proterozoic

28

72

21

79

78

-162

55

171

600

Late Proterozoic

30

70

25

75

80

-177

62

161

660

Precambrian

18

82

18

82

92

176

41

159

690

Precambrian

13

87

19

81

94

171

33

153

750

Precambrian

18

82

38

62

100

156

46

156

Figure 1. Earth showing the side with more continental area (MNA) in the last 750 million years.

Figure 2. Distribution of land areas of Earth today. The figures are divided in four frames, a context paleomap in an equirectangular projection with annotated percent coverage of ocean and lands areas, including how the land is divided between the northern and southern hemisphere (a), the latitudinal distribution of land areas every 15 degrees (b), the viewable land Facing Area (top curve) and Normal Area (bottom curve) as a function of longitude (c), and the longitudinal distribution of land areas every 30 degrees (d).